Currently, there are various techniques being used in the electronic component industry for depositing or plating metal (e.g., copper, cobalt, gold, and nickel) onto the surfaces of electronic components. Such methods include, for example, chemical vapor deposition, metal sputtering, electroplating, and electroless metal deposition.
Electroless metal deposition has become more popular in recent years and involves depositing metal onto the surfaces of electronic components in the absence of an electrical current (i.e., electrolessly).
Examples of where electroless metal deposition has been used in the electronic assembly industry are in the deposition of copper on printed circuit boards. In addition, in semiconductors, electroless deposition is used to deposit nickel on bonding packs, and in multichip modules, electroless deposition is used to deposit copper interconnects.
Electroless deposition of metal is typically carried out by first “activating” the surface of an electronic component by seeding or depositing a substance that will promote metal deposition onto the electronic component surface. However, it is possible that seeding will not be necessary. For example, on a substrate containing cobalt, nickel, rhodium, or palladium, seeding may not be necessary to promote metal deposition. Seeding, when desired, can be accomplished for example through immersing the electronic component in a solution containing a seeding agent.
Following activation, the electronic component is typically immersed in a solution that contains metal ions and a reducing agent. The reducing agent provides a source of electrons for the metal ions, so that metal ions near or at the surfaces of the electronic components are reduced to metal and plated out onto the electronic components.
A wide variety of stabilizers is used today, falling into at least four categories: 1) compounds of group VI elements, 2) compounds containing oxygen, 3) heavy metal cations, and 4) Unsaturated organic acids. Many of the stabilizers currently in use prevent plating on small isolated Cu features, especially under agitated plating conditions, i.e. they do not provide solution stability and small isolated feature plating. Current attempts provide the ability to plate on small isolated features with an unstable plating bath, or provide bath stability without the ability to plate on small isolated features.
Across virtually all applications, there continues to be growing demand for smaller features and increasing performance of integrated circuits. The seemingly endless restrictions and requirements are no more visible than with products in our daily lives. Smaller and denser integrated circuits are expected in many portable electronic products as well as in many larger electronic systems. As the demand grows for smaller electronic products with more features, manufacturers are seeking ways to include more functions within the same or smaller product form factors.
Thus, a need still remains for an electroless deposition system to provide improved stability and small isolated feature deposition. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to save costs, improve efficiencies and performance, and meet competitive pressures, adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.